A secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices. In addition, the secondary battery has attracted considerable attention as a power source for devices which require high output and large capacity, such as electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid electric vehicles (Plug-in HEV), which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuels.
Such devices use a middle or large-sized battery module having a plurality of battery cells electrically connected to each other to provide high output and large capacity.
Preferably, the middle or large-sized battery module is manufactured so as to have as small a size and weight as possible. For this reason, a prismatic battery or a pouch-shaped battery, which can be stacked with high integration and has a small weight to capacity ratio, is usually used as a battery cell (unit battery) of the middle or large-sized battery module. In particular, much interest is currently focused on the pouch-shaped battery, which uses an aluminum laminate sheet as a sheathing member, because the pouch-shaped battery is lightweight, the manufacturing cost of the pouch-shaped battery is low, and it is easy to modify the shape of the pouch-shaped battery.
Meanwhile, a battery module mounted in a middle or large-sized battery pack is generally manufactured by stacking a plurality of battery cells with high integration in a state in which electrode terminals of adjacent ones of the battery cells are electrically connected to each other.
FIG. 1 is a perspective view typically showing an electrical connection structure of a conventional representative battery module.
Referring to FIG. 1, a battery module 50 is configured to have a structure in which electrode terminals 25 of three battery cells 20 are electrically connected to a bus bar 10 in a state in which the battery cells 20 are stacked. The three battery cells 20 are sequentially stacked and are then electrically connected to the bus bar 10, to which other battery cells are electrically connected.
As the number of the stacked battery cells is increased, thicknesses and widths of the electrode terminals and the bus bar are increased. As a result, a large amount of energy is needed during welding.
In this case, laser welding or resistance welding may not be used. Consequently, ultrasonic welding is generally used. In a case in which ultrasonic welding requiring a large amount of energy is carried out, however, ultrasonic waves may be transferred to other regions of the battery cells with the result that the battery cells may be electrically damaged, the lifespan of a welding device may be reduced, and the battery cells may be attached to the welding device.
Consequently, there is a high necessity for a battery module in which battery cells are not damaged through the use of a small amount of energy and electrical connection positions are subdivided to secure reliably connection regions with respect to which various connection methods may be used.